import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import java.util.concurrent.CountDownLatch;

/**
 * @author 郭帅
 * @date 2023/5/20 15:33
 */

public class Main {

    public static void main(String[] args) {
        Set<String> sets = new HashSet<>();
        sets.addAll(null);
        System.out.println(sets);
    }
}
